Telephone-transmitter.



S. G. BROWN. TELEPHONE TRANSMITTER. APPLICATION rum) n. a, 1912Pzitented May 12, 19145 am zs a, m

'UNITED STATES PATENT OFFICE.

SIDNEY GEORGE BROWN, OF LONDON, ENGLAND.

TELEPHONE-TRANSMITTER.

7 '0 all whom it may concern:

Be it known that I, SIDNEY GEORGE BROWN, a subject of the King of GreatBrit ain, residing at 4 Great Wmchester street, in the city and countyof London, England, have invented certain new and useful ImrovementsRelating to Telephone-Transmitters, of which the following is aspecification.

This invention relates to telephone transmitters.

The diaphragm of the ordinary telephone transmitter is peripherallygripped, with the result that since it cannot vibrate uniformly at allpoints on its surface its responsiveness to the acoustic vibrationsfalling upon it is far from being eflicient; moreover it is usuallycomparatively heavy with the result that its inertia makes it sluggishin action. With a view-to rendering the diaphragm more free to vibrateuniforml it has been proposed to provide for flexibility at itsperipheral suppoit, but the essential conditions necessary for highefficiency have not, so far as I am aware, been fullyrealized. Owing tothe great difi'er ence between the density of air and of solidmaterialssuch as are used for diaphragms there isa tendency for a'largepart of the energy of the air vibrations produced by speaking into thetransmitter to be reflected from the surface of the diaphragm upon whichthe air beats. Hence, one of the main essential conditions for adiaphragm is extreme lightness; a comparatively large surfacebeingessential, extreme lightness involves extreme thinness. An extremelythin diaphragm yields to the impacts of the vibrating air, a largepercenta e of the ener of the air being thus absor ed by the su Y stanceof the diaphragm. It is however use less to transfer the energy of thevibrating air to the diaphragm unless the latter is able to transmit itto some point where it can be usefully emplo ed. If, for instance, thediaphragm were a le to vibrate without control, its kinetic energy couldnot be utilized, and it therefore follows that a further main essentialproperty of the diaphragm must be'symmetrical rigidity. A simpleandefficient way of making the diaphragm rigid is to impart to it a conicalshape. xtreme lightness and symmetrical rigi ity are howeverinsuflicient to insure the highest efficiency unless the energy absorbedby the diaphragm and transmitted through its sub- Speclfication ofLetters Patent.

Application filed January 3, 1912. Serial No. 669,150.

Patented May 12, 1914.

' stance is all concentrated at the point where it can be usefullyemployed; for this reason, peripheral support, even if resilient, isinefficient because it presents a ath by which the energy can leak awayt iom the diaphra m to points where no use can be made 0 it. A furtheressential condition, therefore, is that the diaphra m must be supportedonly at its point of symmetry, that is, its center, its peripher beinleft entirely free, or connected to t e inc osing casing merely by aflexible ring of material ofiering no mechanical restraint upon thediaphragm.

According to the present inventionthe diaphragm of the telephonetransmitter is so formedand mounted that the main essential conditionsfor efficiency above stated are realized. The diaphragm is made of lightmaterial, as for example aluminium, and isunusuall thin, the thicknessbeing of the order of 21} t iousandths of an inch. Some idea as to thelightness of the diaphragm may be gained from the fact that if it isallowed to drop to the fall like a heavy mass 0 metal, but moves gentlyor flutters through the air. The diaphragm is shaped to impart rigidityto it, being preferably conical. It is supported by its center, itsperiphery being left entirely free, or connected to a mere flexibleringjof material that offers practically no restraint and no athway forthe esca e of energy. The diap ragm is preferably t ickest at its centerand of gradually decreasing thickness toward its periphery, so that theenergy absorbed by the diaphragm from the adjacent vibratin air isconveyed to the center of the diap ragm with maximum efficiency. Owingto the extreme lightness of the diaphragm, its inertia is small, and itssensitiveness to impressed vibrations is therefore great. In the case ofmaking the diaphragm from a workable met-a1 such as aluminium oraluminium alloy, it may conveniently be spun from a disk into a conicalshape with a flat center piece; by starting the spinning operation atthe edge and working toward the center the desirable result of minimumthickness at the edge and graduated thickness toward the center isobtained. To increase this effect several such disks of differentdiametersmay be assembled into a pile, and these dlsks may if desireddiffer intheir conical angles for increased stifiness. The stiffness orrigidity is from four to six times as'great as the pro-' .of thediaphragm may also be increased, if

desired, by forming radial ribs or corrugations on it. The diaphragm isattached by its center to the mica. disk or other inclosing member ofthe usual granular carbon cell or button forming part of thetransmitter.- i v A further point of importance in obtaining efficiencyin a telephone transmitter is the nature of the air space that isadjacent to the surface of. the diaphragm and contains the air by 'meansof which the vibrations imparted to the air by speaking are conveyedthrough the aperture .at the base of the usual mouth piece and up to theactual surface of the diaphragm. In this connection particular careshould be taken in the formation :of the space between the narrow end ofthe mouth piece and the actual surface of .the diaphragm; this spaceshould be such as to maintain the pressure conditions existing at thenarrow endof the mouthpiece and thus prevent any appreciable loss inenergy transmission by a sudden drop in pressure or otherwise. In orderto reduce the excessive amount of space presented by a conicaldiaphragm, the cover piece to which the narrow end of the mouth piece isattached is conveniently coned inwardly on its inner face so as toconform approximately to the shape of the diaphragm. According to afurther feature of the present invention, therefore, the amount of airspace adjacent to the surface of the diaphragm is in some casespurposely reduced, below what it would be in the case of a conical ordished diaphragm and a flat cover piece, by shaping the inner surface ofthe latter to correspond to some extent to the contour of the diaphragm;for instance, in the case of a conical diaphragm, the inner surface ofthe cover piece may be formed conically also.

It has been found in actual practice that the proportion of energytransferred from the air to the diaphragm in a telephone transmitterconstructed as above described portion transferred in the ordinarytransmltter in common use at the present time.

In the accompanymg drawings :Figure 1 is a sectional elevation of oneform of' granular carbon cell transmitter constructed in accordance withmy invention. Fig.2 shows a modified construction in which a bladespring is provided to control the diaphragm. Fig. 3 is a sectionalelevation of a button type of transmitter, and Fig. 4: a solid-back typeof transmitter constructed in accordance with the invention.

Fig. 5 is a sectional elevation and Fig. 6 a plan of a transmitter inwhich the diaphragm is supported at three points instead of at itscenter. Fig. 7 is a sectional eleva tion of a granular form of thetransmitter in which the diaphragm is trumpet-shaped inpiece, D thediaphragm, and E the variable resistance device within the casing A.

In the construction shown in Figs. 1 and 2 the variable resistancedevice E is the ordinary granular carbon cell, and the flat center pieceof the conical diaphragm D is secured to the mica disk E of the deviceE. To the opposite face of the mica disk a sheet of carbon is secured,and this sheet may if desired be ribbed or corrugated or otherwisestiffened so as to increase the. strength and rigidity of the centerportion of the diaphragm as well as to effect a good electrical contactwith the contents of the cell. The air space in front of the diaphragmis preferably separated completely from the air space behindthediaphragm by a thin ring D of pliable material fastened to theperiphery of the diaphragm and to the body of the transmitter, orpreferably to a removable ring clampedbetween the cover iece and thecasing. This ring D may be ormed of tissue paper of say l/3000 of aninch thick, the essential condition being that the ring should benarrow, thin, and resilient, so as to absorb as little energy aspossible from the free edge of the diaphragm. Preferably, the ringconsists of an extremely thin ring of collodion and is attached to theperiphery of the diaphragm and to the removable ring by placing thecollodion ring in position'and paintmg its edges with liquid collodionwhich dries up and establishes a firm joint. The thin solid collodionmay be formed by spreading outa quantity of liquid collodion on a sheetof glass and allowing the collodion film so formed to solidify bydrying.

In Fig. 2 the diaphragm D instead of being controlled or restrained inits movements by a mica disk,- is secured to ablade spring F, to whichalso is secured a carbon disk E The said disk E is peripherallyuncontrolled and bears upon carbon'balls or granules located within andconstituting part of the variable resistance device E The carbon disk Emay be connected to other parts of the blade spring than that shown, sayto a point nearer its point of support, if necessary; also any otherform of carbon cell maybe employed.

In Fig. 3 the, diaphragm D is shown connected to the common button typeof variable resistance device. p I In theconstruction shown inFig. 4 thecarbon cell is of the kind in which the face of the lower block iscircularly notched, as" shown in dotted lines. The upper block or meat-wcarbon coated on the back with a thin layer of copper, has fixed to it asmall base plate E from which projects a screw-threaded center post. E".The conical diaphragm D, instead of being rendered especially stifl atthe center by being thicker there, may be of uniform thinness, the greatstiffness at the center being obtained, as shown, by raising the centerinto the form of a cone, the'diaphragm being then held in position bythe engagement of the flattened apex of this conically formed centerwith the aforesaid center post E. Thus, the whole vibrating mass is ofgreat lightness. The V-shaped channel between the two oppositelydirected conical surfaces rests upon the back of the upper block orplate of the carbon cell, pinching the supporting plate of mica betweenit and the said block or plate.

In the arrangement shown in Figs. 5 and 6 the channel between the twooppositely directed conical surfaces of the diaphragm D is flattened,and the diaphragm is attached at three triangularly spaced points tothree carbon cells mounted in an insulating (ebonite) support. Thesecells may work in series or in parallel, depending upon the manner inwhich the connections are made. If they work in parallel, the diaphragmmay of course have electrical connection with each of the cells, but, ifthey work in series an insulating washer must be placed between thechannel of the diaphragm and one or-more of the carbon cells. The meansshown in the figure for holding down the diaphragm consist of aplate andpost such as those shown in Fig. 4 at E and E re spectively, and aspring washer E located beneath the channel of the diaphragm.

The chief feature of constructional importance in the transmitter shownin Fig. 7 is the trumpet-like formation of the main part of thediaphragm.

Fig. 8 represents a further constructional form of transmitter with atrum et-shaped diaphragm. In this case the car on cell is shown ashemispherical and the diaphragm is open-ended, the circumference of itssmaller end bein attached to the circumference of the henusphericalcarbon cell. The cover piece B is made to conform in shape 'to thediaphragm. The conformation of the inner surface of the cover piece Bwith the contour of the diaphragm is desirable in the case of atransmitter of the design shown in Fig. 8, or in any case where theinstrument is rather large and the space corresponding to the depressionof the diaphragm is in consequence large, but where the trahsmitter isof the dimensions corresponding to Fig. 2, for instance, which is fullsize, the cover piece need not be specially designed in this respect.

As hereinbefore stated, thediaphragm is preferably of graduatedthickness from the center outward, the minimum thickness being at theperiphery. If desired, several hat I claim and desire to secure byLetters Patent of the United; States is:-

1. A telephone transmitter comprising a variable reslstance device, acasing containing said device, a mouth piece carried by the casing forconveying sound waves into the same, a light, peripherally unrestrainedconical diaphragm the thickness of which averages a few thousandths ofan inch but decreases rogressively toward the periphery, and meanssecuring the diaphragm at its central region to the" movable member ofthe variable resistance device.

2. A telephone transmitter comprising a variable resistance device, acasing containing said device, a centrally perforated cover piece on thecasing, a mouth piece carried by the cover piece, a li ht, peripherallyunrestrained, conical diap ragm the thickness of which averages a fewthousandths of an inch but decreases progressively toward the periphery,and means securing the diaphragm by its center to the movable member-ofthe variable resistance device.

3. A telephone transmitter comprising a variable resistance device, acasing containing said device, a centrally perforated cover piece on thecasing, a mouth iece carried by the cover piece, a peripheral yunrestrained, conical dia h'ragm of aluminium the thickness of whichaverages two and a half thousandths of an inch but decreases piogressively toward the periphery, and means securing the diaphragm by itscenter to the movable member of the variable resistance device.

4. A telephone transmitter comprising a variable resistance device, acasing containing said device, a mouth piece. carried by the casing forconveying sound waves into the same, a light conical metal diaphragm thethickness of which averages a few thousandths of an inch but decreasesprogressively toward the periphery, means securin the diaphragm by itscenter to the mo'vafile member of the variable resistance device, and aring of flexible material of the order of one three-thousandths of aninch thick, connecting the periphery of the diaphragm to the interior ofthe casing.

5. A telephone transmitter comprising a variable resistance device, acasing containing said device, a centrally perforated cover piece on thecasing, a mouth piece carried by the cover piece, a conical aluminiumdiaphragm the thickness of which averagestwo and a half thousandths ofan inch but decreases progressively toward the periphery,

.means securing the diaphragm by its center and a half thousandths of aninch but decreases progressively toward the periphery, means securingthe diaphragm by its center to the movable member of the variableresistance device, a removable flange within the casing, and a ring ofthin film collodion connecting the periphery of the diaphragm to theflange. I

" 7. In a telephone transmitter, a variable meaew resistance device, alight, conical, peripher ally unrestrained diaphragm having its centralpart coned in the opposite directionto the main part, and means forconnecting the central part of the diaphragm to the movable member ofthe variable resistance device.

8. In a telephone transmitter, a variable resistance device, a lightconical diaphragm having-its central part coned in the oppositedlrection to the main part, a base plate secured to the movable memberof the variable resistance device, a screw-threaded center postprojecting from said base plate, and

means for securing the central part of the diaphragm upon the saidcenter post.

In testimony whereof I aflix my signature in presence of two witnesses.

SIDNEY GEORGE BROWN. Witnesses:

T. SELBr WARDLE, W. J. SKERTJEN.

